The present invention pertains to a two-chamber step bearing with hydraulic damping especially for mounting the engine in motor vehicles.
Various designs of two-chamber step bearings have been generally known from the state of the art. A membrane of varying hardness and ductility may be arranged between the working chamber and the compensating chamber in some hydraulic step bearings. Such a membrane is usually called a coupling membrane, and the degree of mobility of the membrane determines the vibration amplitude which can be influenced, and the stiffness of the membrane determines the frequency of the vibration to be damped. If such a membrane is relatively soft, the vibrations acting on the hydraulic fluid of the working chamber are transmitted without resistance to the adjoining compensating chamber. However, if the membrane is provided with a relatively stiff structure, the vibrations acting on the hydraulic fluid will build up an overpressure in the working chamber, and this overpressure leads to a swelling of the uncoupling membrane and thus guarantees better damping, but a higher dynamic stiffness develops at the same time. It is desirable in the two-chamber step bearings known from the prior art for adaptation to different operating states to correspondingly adapt the vibration behavior of the hydraulic bearing to these operating states.
This is of significance especially because the disturbing vibrations generated by the engine during the operation of the vehicle occur essentially in two different forms and therefore require different stiffnesses of the engine mounts used for vibration damping. The different damping properties are of great significance especially in the direct-injection diesel engines that have been used for some time now because the vibrations occurring at idle in these engines are higher than in the diesel and gasoline engines used hitherto in automotive engineering, so that an especially soft engine mount is necessary for the operation at idle for vibration damping in these diesel engines, whereas a substantially stiffer engine mounting is advantageous for vibration damping in the drive mode.
Adaptation can be achieved in the above-mentioned two-chamber step bearings provided with an uncoupling membrane between the working chamber and the compensating chamber, e.g., by changing the stiffness of the membrane by, e.g., reducing or increasing the support diameters of the membrane. This can be brought about, e.g., by means of a motor operator with a plunger actuated by same, which presses the uncoupling membrane from below. However, the different spring stiffnesses necessary in the above-mentioned direct-injection diesel engines cannot be achieved with the two-chamber step bearing known from the state of the art because the values of the required spring stiffnesses have an excessively great difference.
A prior-art two-chamber step bearing, which is formed by a first hydraulic damping spring element, a spring element, at least one fluid-filled working chamber and at least one compensating chamber connected to same by an overflow channel, wherein an additional, blockable spring element, which is arranged in a separate pretensioning chamber is arranged in series after the said damping spring element, has been known from, e.g., DE 43 22 958 A1.
In addition, an additional spring element with a hydraulic functional connection with a first hydraulic damping spring element has been known in a two-chamber step bearing from JP Abstracts 62-270 841 (A), but the spring element disclosed in this document cannot be controlled or blocked.
The object of the present invention is therefore to improve a two-chamber step bearing with hydraulic damping especially for mounting the engine in motor vehicles such that it is also possible to achieve the very great differences in the spring stiffness of such two-chamber step bearings for the drive mode and operation at idle, which are required in the case of the use of modem diesel engines. In addition, such two-chamber step bearings shall have a compact design and their manufacture shall be inexpensive and they shall operate reliably under all required operating conditions.
This object is accomplished corresponding to a first solution variant by the pretensioning chamber having the blockable spring element being hydraulically connected to the working chamber and the compensating chamber via at least two switching elements that can be controlled independently from one another. Due to the vibrations introduced by the engine into the two-chamber step bearing, the pretensioning chamber can be filled up with a hydraulic fluid, which makes possible the blocking of the additional spring element.
Another solution variant for the object is disclosed by the technical teaching of the pretensioning chamber being connected to the compensating chamber by a first line, in which a pumping device is arranged, which is driven by the vibrations introduced into the two-chamber step bearing and is provided for filling up the pretensioning chamber with hydraulic fluid, and by a second line with an electromagnetic on-off valve inserted therein.
Due to the embodiments according to the present invention corresponding to the two possible solutions, blocking of the second spring element, which is connected in series with the first damping spring element, is brought about as needed by the vibrations of the engine only, whose vibrations are to be damped by the two-chamber step bearing, and which vibrations are introduced into the two-chamber step bearing, without an external power source.
Due to the blocking of the additional spring element, the overall stiffness of the engine mount is substantially greater than when both spring elements connected in series are active. As a result, both a soft damping characteristic for the idle operation of a motor vehicle engine and a stiff damping characteristic for the normal drive mode are provided in the two-chamber step bearing according to the present invention. The blocking of the additional spring element can be eliminated via the switching element, which is present between the working chamber and the compensating chamber and which is preferably an electromagnetic on-off valve by a pressure equalization being brought about between the pretensioning chamber and the working chamber or the compensating chamber.
Special other embodiments of the first solution according to the present invention providing one switching element as the nonreturn valve arranged between the working chamber and the pretensioning chamber and providing one switching element as an electromagnetic on-off valve arranged between the compensating chamber and the pretensioning chamber. Special embodiments according to the second solution include providing the pretensioning chamber connected to the compensating chamber by a first line, in which a pumping device, which is driven by the vibrations introduced into the two-chamber step bearing and is provided for filling up the pretensioning chamber with hydraulic fluid, is arranged, and by a second line with an electromagnetic on-off valve inserted into it and by providing the pumping device with a plunger piston and a nonreturn valve, wherein the said nonreturn valve is arranged between the plunger piston and the compensating chamber and provides a possibility of flow from the compensating chamber to the pretensioning chamber.
In addition, additional advantageous embodiments of both solutions according to the present invention may employ the blockable spring element arranged between a partition, which forms a wall of the compensating chamber, and a movable bottom plate, which forms a wall of the pretensioning chamber. The said blockable spring element may comprise at least two, preferably three coil springs arranged concentrically to the central longitudinal axis of the two-chamber step bearing.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated.